I only used one text field here, but otherwise I think this what you want as a starting point:

#!/usr/bin/perl -W
use warnings 'all';
use strict;
use Tk::Pane;

my %data;
while (<DATA>) {
  m/^(.)(.+?)\s+$/ and push @{ $data{"\u$1"} }, "\u$1\L$2";
}
my $mw = Tk::MainWindow->new();
my $left_pane = $mw->Scrolled(
  'Pane',
  -scrollbars => 'oe'
)->pack(
  -expand => 'yes',
  -fill   => 'y',
  -side   => 'left',
);
my $right_pane = $mw->Scrolled(
  'Pane',
  -scrollbars => 'oe'
)->pack(
  -expand => 'yes',
  -fill   => 'y',
  -side   => 'right',
);
my $middle_pane = $mw->Scrolled(
  'Pane',
  -scrollbars => 'oe'
)->pack(
  -expand => 'yes',
  -fill   => 'x',
  -side   => 'top',
);
my $mid_entry = $middle_pane->Scrolled(
  'Entry',
  -relief      => 'sunken',
  -scrollbars  => 's',
)->pack();

my @right_list;
sub alter_mid_and_right_panes {
  my ($key,$value) = @_;
  return unless $value;  # Don't change when unchecking left box.
  while( my $cb = pop @right_list ) {
    $cb->destroy();
  }
  $mid_entry->delete(0, length($mid_entry->get()));
  $mid_entry->insert(
    'end',
    "Ah, '$key'.  What a great letter! I remember her well."
  );
  for my $word ( sort @{ $data{$key} } ) {
    my $cb = $right_pane->Checkbutton(
      -anchor   => 'w',
      -text     => $word,
    )->pack(
      -side => 'top',
      -fill => 'x',
    );
    push @right_list, $cb;
  }
}

my @list;
for my $key ( sort keys %data ) {
  my $value;
  my $cb = $left_pane->Checkbutton(
    -anchor   => 'w',
    -text     => $key,
    -variable => \$value,
    -command  => sub { alter_mid_and_right_panes($key, $value) },
  )->pack(
    -side => 'top',
    -fill => 'x',
  );
  push @list, \$value;
}
Tk::MainLoop();

__DATA__
Abe
Apple
Baker
Bananna
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